pixelation problems

There is one tv in my house that is having severe pixelation problems. It is the tv attached to the master dvr box. The other tv's are fine, internet apps on affected tv is fine. Pixelation makes watching sports impossible. I have reset all boxes, modem, and checked all cables. I am looking for a solution. Xfinity support is a nightmare, I dread having to deal with them again. I have wasted hours and hours on them, and no one seems to have a clue, and they dont communicate with each other. Anyone have any suggestions before I go into [Edited: "Language"] Xfinity support.